The oil and gas industry has adapted electrical and mechanical equipment for service in a subsea environment. This adaptation involves the installation of heat producing equipment into pressure vessels which are have limited interior space. A pressure vessel, as used herein, is a closed container designed to hold gases or liquids in a pressurized environment. For example, an internal pressure of the subsea pressure vessel may be maintained at about 1 ATM, whereas the pressure outside the subsea pressure vessel may be many ATMs (which is dependent upon at least the depth of the water). The pressure vessel is configured to house a heat producing apparatus associated with oil and/or gas production.
Cooling of heat producing equipment, in a non-subsea environment, is conventionally provided by radiation or natural convection cooling to the surrounding air. Removal of heat can be critical to the reliability, longevity and performance of some equipment. Forced cooling methods (e.g. either liquid or air) require periodic intervention and maintenance, such as replacement of fans, the repairing of leaks, or the addition of coolant.
Conventional practice for adapting equipment for subsea applications includes the use of active heat transfer devices (e.g. pumps, and fans) and components (e.g. filters, fittings, valves, connectors, etc.). For example, interior cooling fans that circulate air as a cooling medium are used in combination with an “active” (meaning with moving mechanical parts and/or requiring electrical power) cooling means. The active cooling means often includes pumps and a heat collection system located on the interior side of the pressure vessel, a penetration through the pressure vessel, and a heat expulsion device (e.g. radiator, exchanger) in communication with the motive device (e.g. pump). These systems typically exchange heat via convection or radiation only via a medium in substantially a single phase only: liquid, in the case of a pump, and air (gas) in the case of fans. The active components contribute to high rates of failure and a need for periodic maintenance. These systems lack the reliability and the ultra-low maintenance requirements desired for subsea applications. The liquid cooling systems often utilize de-ionized water as the cooling medium due to its low electrical conductance as required to cool high power electronics, The use of de-ionized water in forced cooling systems, creates a need to control and maintain water quality and it's contamination levels, a task typically requiring manual intervention and maintenance. The reactive nature of de-ionized water also can cause corrosion leading to leaks and failure in cooling water containment systems, piping, fittings, pumps, seals and other components. Having a subsea system containing heat producing components with the passive cooling of this invention overcomes the issues created by systems requiring forced cooling medium. An advantage of liquid filling the subsea vessel with a dielectric fluid is that it extends the life of the contained equipment by improving heat transfer and by reducing oxygen levels thus reducing corrosion potential on components such as electrical terminations.